


Illyasviel von Einzbern's Birthday Party

by Gothdresser



Category: Fate/stay night - All Media Types
Genre: ABDL, Birthday, Birthday Fluff, Diaper, Gen, Giving Illyasviel the proper birthday that she deserves~, Omorashi, Pantypoop, Pee, Pool, Soiling, Wetting, diapermessing, messing, padding, playground, poop, poopy pampers, store
Language: English
Status: Completed
Published: 2019-12-21
Updated: 2019-12-21
Packaged: 2021-02-24 16:34:14
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 7,575
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21881062
Author URL: https://archiveofourown.org/users/Gothdresser/pseuds/Gothdresser
Summary: Blowing out the candles on her cake, Illya makes quite the unconventional birthday wish, leaving Sakura and Rin to help grant her adorable wish throughout the day~A month late, but finally finished, as well as another story to make up for the lateness with Illya probably having eaten a little too much cake...~Enjoy this and the other story~
Relationships: Illyasviel von Einzbern & Irisviel von Einzbern, Illyasviel von Einzbern & Matou Sakura, Matou Sakura & Tohsaka Rin
Kudos: 16





	Illyasviel von Einzbern's Birthday Party

Planting the last of the cherries on top of the cake, Rin wiped the sweat from her brow and grinned at the finished product. Although she liked sweets, she hadn’t done too many complex cakes before and Sakura more than helped her out with this beautiful chocolate creation. Based on the Einzbern family’s regional origins, she had gone after the german black forest cake that Sakura had recommended, struggling with the tiered cake to finally finish it.

Just in time too as she lined up various candles around the text that read, “Happy Birthday!” To think that Illya didn’t really celebrate her birthday very much, just a small occasion with her maids… Rin had already felt uneasy when Illya had offhandedly mentioned it, but something lit up in Sakura’s eyes and she knew that she’d be roped into this one way or another. She had even let them host the party at her house for lack of a better location, not that the Matou residence would have been better. Plus, that meant Rin got to use her kitchen for once, and quite a lot too as she lit the candles on the cake and began to carry it out.

Rin nodded to Sakura as she brought out the cake and both girls joined together in song. “Happy birthday to you! Happy birthday to you! Happy birthday, dear Illyaaa! Happy birthday to yooooou!~” The pair smiled together as the excitement of the little girl was more than obvious already, knowing they had done well.

“Oh! Oh! It looks so amazing!” Illya scanned all around the cake, sitting up off of her chair while beaming, such a large cake all to herself or as much as she wanted of it. Giggling, she sat back down and squirmed a bit in her chair, as if the excitement or possibly something else wouldn't let her sit still, her loli butt shifting from cheek to cheek. “You really mean it, right? Anything I want when I blow out the candles?”

"Of course, it's your birthday, after all. Nee-san and I are here for you, so we'll do our best to make your birthday dreams come true~" With Rin rounding the table on one side to stand next to Illya, Sakura followed suit to mirror her. She hadn't been in the position to celebrate her birthdays before, so while she had to rope Rin into it a bit, Sakura was more than happy to throw a party for the little girl, only giving the trio another reason to hang around together without their servants. Rider might have been alright to join them, but if she came, Saber would want to as well and the cake was meant to be for Illya, not as a tribute to the King of the Britons. "So, go on, anything you want and we'll make it happen as well as we can!" Joining the petite girl in a strong smile, Sakura could not have expected the result that would come as she heard Illya giggling.

Lifting her butt off of the chair to lean closer to the candles, Illya’s grin was as wide as it was mischievous. “Hehe, well… I want to be the birthday baby for all of today!” Breathing in deeply, she blew out every single candle of the cake on the first try before her face turned red and Illya blew out her panties. The little girl’s face scrunched up as she softly grunted, the crackling of the candles being replaced with distinct crackling from her big loli butt before it evolved into squishing. Quickly, a big stinky mess poured out of her, stretching her tight little butthole to tent then bulge out her panties, giggling mixed with groans as Illya made sure to get every little bit out of her and into her underwear. Rin and Sakura could only watch on as their mouths hung open, their silence overwhelmed by the sound of the head of the Einzbern family utterly shitting herself for over a minute, finally coming to an end as she huffed and puffed to catch her breath. “All done making stinkies~” And without missing a beat, Illya lifted the back of her skirt before sitting right down on her brown bulging butt, a muffled but resounding squelch coming from underneath her.

The pair of sisters just looked between each other for a few moments, with Rin gesturing to Sakura if what they had just heard had really happened, but it was Sakura who spoke up finally. “Quite the wish, wouldn’t you say, Rin? We did say we’d make her birthday wish come true though, and I think the birthday baby needs a change. Let me just make sure though~” While Rin just continued to stare at her in disbelief, Sakura lifted up the back of Illya’s skirt, and even she had to do a double-take as it amazed Sakura that such a little girl could poop herself so much as the underwear squished and stretched out, made worse by Illya sitting in it.

Although it was already so clear what Illya had done, Sakura still used her free hand to pull open the back waistband of Illya’s pink-turned-brown panties, wishing she had an extra hand to hold her nose. “Pee-yew, such a stinky girl~ Did that feel good to go potty like a proper baby?” With such a mess though, Sakura turned her attention back to her sister, knowing that she shouldn’t leave Illya in such terribly soiled underwear for too long. “Nee-san, if you have any wet wipes in the bathroom, could you grab them for me? And a pair of panties too, the smaller the better since I imagine a little baby girl wouldn’t fit in our sizes.” Maybe Illya would fit in their panties from about a decade ago, although the question of if those were still in the house came to mind, depending on how sentimental Rin could be.

It took Rin a few moments as she processed everything that was happening, slowly nodding to Sakura before heading to the bathroom for the wipes. Good thing she kept them stocked in her house since they were what she preferred after the bidet incident, not wanting anything close to a repeat of that. However, as Rin headed into the only room that might have any semblance of panties for a little girl, she found that while most of Sakura’s old room had been untouched, the drawers were emptier than she had guessed. “Crap…” Sakura wasn’t the happiest when Rin let her down, often showing a darker side to her but Rin prayed that taking care of Illya would keep her calm. Well, as calm as Sakura could be as Rin slinked back downstairs.

“Say ‘aaaahh’” Lifting another fork up to the little girl’s mouth, Illya gladly accepted what Sakura was offering, almost through a whole slice of cake by the time Rin got back. The little girl wanted to be the baby, after all, and who was Sakura to deny that when enabling it allowed such an adorable display. Illya was even a couple of years older than Sakura, and yet Sakura was the one to be a sort of big sister taking care of her baby sister. Someone else was supposed to fulfill the former role since she was an actual big sister, but it wasn’t too surprising when Rin came back almost empty-handed. “Only the wet wipes? Were there really no panties?” Rin wasn’t usually a meek girl, but Sakura noticed her turn her head slowly side-to-side, an obvious sign that she didn’t want to upset her sister. “Oh well, guess we need to take the little baby girl to get some diapees~ Rin, how far away is the closest store?” Surely Rin could manage that at least while Sakura continued to feed Illya to finish off her slice of cake.

After encountering the problem of a lack of smaller panties before, Rin was relieved to have seen nothing cropping up around her sister’s face. Maybe Illya really was a good solution for Sakura’s not-so-nice side, although that only depended on how long Illya wanted to be like this. A day would already be so nice, and Rin wondered how much convincing it would take to extend Illya’s fun for more than just a single day. “The store is just down the street, within walking distance too. We can head out anytime then.”

“Perfect, let’s get on our way then, and you can have more cake when you get back. Is that alright with you, Illya?” Getting a nod from the small girl, Sakura wiped away a little bit of chocolate on her cheek before lifting her off of the chair, an obvious stain having been left. Leading her over to the door, she even helped Illya get her boots on, the motherly role seeming all too natural to Sakura. With all their shoes on, the three girls headed out of the house and made their way down the street.

Rin couldn’t help but notice how playful Illya was during all this, a new side to the little girl she hadn’t really seen before compared to her viciousness during the grail war. Sure, during the right moments, Illya could get rowdy and at least one vase had been lost to her running around, but not this sort of… childishness, something that Rin herself hadn’t had much of a chance to experience either. She'd never admit even a shred of jealousy though as her mind wandered while the trio had already made decent progress on their walk.

Nearing the store and between her two new caretakers, Illyasviel tightly held onto their hands, humming with a smile plastered on her face. It had been a whole, tough decade since she had last felt this happy, although the messiness had surfaced occasionally when she sometimes pushed her little body a little much. The big difference was that this time she wasn't shitting herself out of temporary incontinence but rather unloading in her underwear of her own free will. A free and stinky will that she certainly intended to exert as much as she could today, especially when they finally arrived and she hurried away from Rin and Sakura.

"I-Illya, wait up! Rin, go after her!" Sakura's cry was met by giggling from the young girl, and Rin hesitated for but a moment until she saw the look in Sakura's eyes. There was no way she was disobeying that and a black skirt fluttered after the silver-haired loli. She had to be here somewhere as Rin took a few minutes going aisle by aisle, but if Illya wanted to be a baby, then there was only one aisle she had to be in.

And heading immediately there, Rin was proven right as she saw Illya standing amidst the various brands of baby diapers, but… o-oh no… "Illya, hold on. We can get you to a bathroom, just w-... a-ait…" The signs were clear with Illya shifting from foot-to-foot, one hand at her crotch while another was at her rear. It was absolutely too late though as Rin saw a light golden liquid splash onto the ground between the purple boots.

Illya had found herself just a little too excited for her diapers, but Rin and Sakura could catch up to her as she scanned the various signs hanging over the aisles. She had a vague idea where they might be already since this wasn't the first time she had been here while visiting Rin, but this was the first time she dared venture into the diaper aisle, her eyes lighting up at all the colorful packages. There were certainly some that wouldn't fit her since she wasn't a newborn, but a girl like her could still fit in one of the larger sizes. However, her bladder reminded her of a certain need while searching, holding off the need until she found the right size diapers.

But she didn't move her body to go grab them, taking a deep breath instead and waiting for a moment to feel that hint of desperation. If she was going to be a baby today, this was something she had to get used to, letting go as she heard a shout to her side. Lucky Rin, she got to see a fuller accident than the one Illya had on her expensive chair~ There wasn't much reason to hold back as Illya's face scrunched up and turned a little red, her body starting to slightly crouch while her little peepee let out quite a lot of peepee to flood her panties. The warmth partly flowed down her pale legs while the majority splashed onto the ground beneath her, a puddle growing around where she stood.

To make her fun even better, Illya was glad to have eaten that slice of cake before they left as she felt a familiar pressure at her rear, packing her panties, even more, the moment she felt the need to. Stinky would be an understatement for her with her undies sagging down near her knees now, the fact that they still managed to contain two big messes was nearing a miracle on the level of true magic. Rin hurried up right now to her though as Illya giggled and was red in the face. “Uh oh, I had an oopsie. I thought I could last until my diapees, but I really had to go peepee and uh,... hehe~”

Stopping a couple of feet from the little girl, Rin shakily lifted her hand as her mind was racing to figure out what to do. She had lost sight of Illya for a few minutes, and in such a small frame, she had such a large accident. Or, well, Rin had to wonder how much of today was going to be accidents and ‘accidents’, although that didn’t matter too much as Illya admitted to wetting herself, but did she… Her hand was already extended and Rin could hear just a slight squish as Illya’s butt wiggled back and forth, and the lift of the skirt revealed the inevitable: Illya had pooped herself… again… “I know you wanted your diapers so much, but couldn’t you have gone to the bathroom first instead? Or you should have at least said something, you’re still older than I am and yet you crapped yourself.” Illya really wasn’t going to make this easy on her, and Rin struggled to imagine why this girl was smiling and giggling after she pissed and shit in her panties.

Rin came close to doing the former in her own underwear though as she felt a hand on her shoulder, ice-cold even through her turtleneck. “Ooooh, Riiiin~ You’re not making fun of the birthday girl and what she wants, are you?~” That voice wasn’t exactly Sakura’s and Rin lost her own voice as she shook her head side-to-side, shivering despite the hand being lifted. Sakura could be utterly scary all too often, and yet as her younger sister passed her to squat down and check Illya herself, there was no trace of anything darker. “I see you got a little too excited for your diapers, hmm, Illya?” The little girl shifted in place with a big grin on her face as Sakura pulled out the back of her panties, going a bit far by feeling the double bulge and checking around the front as well. She really was thorough after all, and while Rin had gotten lost in watching the check, the tsundere straightened back up when she got a side-eye from Sakura. “Go buy the diapers and meet us in the bathroom. Hurry too, you’re cleaning her up for the rest of today if Illya goes potty again before getting her diaper on~”

It seemed to only be around Sakura that Illya could see Rin in such a cowardly position, almost right away grabbing the cute baby-print diapers that Illya had been looking at before hurrying off to the front of the store. To think that the older sister was so whipped by the younger sister, but it wasn't like Illya hadn't seen how scary Sakura could be. Still watching down the aisle where Rin had hurried off, Illya was surprised to find herself scooped up off of the ground. If she hadn't felt like a baby already after pooping her panties twice and pissing them as well, then the wetness dripping from her crotch as Sakura carried her on one arm did. She was curious if Sakura was enjoying her wish more than she was, letting the violet-haired girl carry her all the way into the bathroom.

However, instead of being set down on the ground, even Illya found herself blushing a little as Sakura pulled open the baby changing station and laid her down on it. It made Illya happy to think she was going so far, even removing her skirt to avoid ruining it, leaving her in just a dress shirt and with poopy panties on full display. Anyone could walk in and see how a girl who looked to be in at least middle school had completely ruined her panties, a soft squishing coming from under her butt as Illya was beginning to feel a touch of the embarrassment of her birthday wish. Yet that anxiousness quickly faded away as she found her hair being petted, a soft humming coming from Sakura as they waited a few minutes together until the bathroom door finally opened.

“Sorry that took so long, the lines were longer than I expected and those self-check-outs are always so stupid when they don’t work right." Surpassing her technological troubles, Tohsaka still made it to the bathroom as fast as she could with the bag of diapers, an embarrassment of her own stemming from the fact that she bought them in front of so many people, even if they weren't for her. They were obviously not her size as well, but the idea of buying the diapers was something that she was very glad was done and over with, handing off the bag full of padding and other changing supplies to her sister.

With Sakura glancing over the items, Rin was relieved to see a smile on her face, hoping this would be the last of the second-hand embarrassment she'd be getting today. "Oh, you got some wet wipes and baby powder as well. Good job, Nee-san~" Sakura pulled out the contents of the bag and laid it on the table next to Illya, the little girl combing over them as well. "Wandering eyes, hmm? Don't worry, I'll make this quick and we can head out of here, especially now that we have diapers for the birthday baby. Any place that you might want to go to, Illya? Even if we're changing your diapers, feel free to lead the way~"

Lying on the baby table while Sakura proceeded with the change, Illya contemplated exactly what she wanted to do today, somewhat unsure as she hadn't even fully expected to get this far. Sakura really was going above and beyond, and Rin was roped in as well, even if a bit begrudgingly. "Hmm, it might be a little far, but there's that pool, and uh… Oh! The nearby park too, yeah yeah!" Wiggling on the table, the little girl was steadied by Sakura before the latter removed the incredibly poopy panties, the remaining mess surprisingly not too bad.

"Nee-san, dispose of these, please. I don't think Illya is going to need them anymore, or that they can even be saved… Such a stinky little girl~" With Illya giggling a little at the compliment and the panties handed off, Sakura opened up the wet wipes and carefully wiped the big loli butt clean. Although there wasn't much left of the mess, Sakura still made sure Illya was thoroughly cleaned, the towelette parting her buttcheeks and shaping to the curves of her rear until Sakura was satisfied with the cleanliness. "Sure, we can easily do that, both even. The park is closer to the store, but we should get to the pool sooner rather than later. I'm almost done now too, Illya~ and Rin, can you please call a taxi for us so we don't have to wait as long?"

Sakura seemed to be in full caretaking mode as far as Illya could observe, Tohsaka not even piping up with her objections anymore while Illya felt her rear lifted up just a little for the soft crinkly diaper to be slipped underneath her. To think that after a whole decade, she'd actually get the chance to be diapered in a positive situation, rather than any temporary incontinence caused by the command seals or… less than pleasant dreams… None of that mattered now though as she could barely contain her excitement with the baby powder being applied and her crotch finally being enveloped with the padding she so very much wanted.

With some checking of the leg guards and a couple of pats to the front of her diaper, Illya's smile went on for miles as she sat upon the changing table, feeling the soft fuzzy feeling of the babyish underwear emblazoned with cartoon characters. "Thank you very much, Sakura! And you too, Rin! Today is going to be so much fun~" She just couldn't help her beaming as Sakura helped her off the table, but Illya stopped her as she was about to put the rest of the pack of diapers back in the bag. "Oh, may I please hold those?"

For whatever reason Illya might want to, neither Sakura or Rin knew but they didn't let that stop the little girl from wrapping her arms around the package of padding, escorting her out like that. "You're the birthday girl, after all. And the taxi was nearby, so it should be waiting outside of the store any minute now." Rin began to lead the way out of the store, but as she turned back to make sure Illya was following, she realized something all too important. "Eh? What happened to your skirt?"

Both Illya and Sakura looked down to see the former wearing nothing but her shirt and diaper, the little girl too caught up in the euphoria of her pampers that she hadn't realized that she was still undressed. Sakura was on top of it though as she pulled the skirt out of the bag, absentmindedly having put it in with the supplies. "Would you like me to put your skirt back on Illya?" There was a moment of hesitation, but the silver-haired girl nodded and Sakura slipped her skirt back up around her waist, concealing her diaper. "Rin, take Sakura out to the taxi, I want to look around quickly myself~"

With their motherly figure heading off towards a small clothing section of the store with the other changing supplies in her bag, Rin took Illya out of the store and towards where she had requested the taxi to arrive. It took more than a few minutes of awkward silence between them, but the timing was perfect as Sakura came out of the store just as the taxi pulled up at the curb before them. With the three girls climbing in, the cab lurched forward and buzzed off across the bridge to Exciting Splash. At least they had done the party earlier in the day by Illya’s request, leaving the afternoon and evening free for various events.

The drive wasn’t meant to take too long, but soon after they had taken off, Sakura began to notice that Illya’s legs were squirming with her hands pressing a little too much in her lap. Such a silly girl, especially since she was the one that had wanted to be diapered so badly. “We don’t know how much longer it’ll be, Illya. It’s alright, just do what you need to~”

Despite how gung-ho she had been with getting her diapers, enough to have reluctantly put them in the supply bag once they had gotten in the taxi, there was this hesitation that she had with the clean crinkly diaper. Her panties had been super easy to poop in, especially since she had been practically bursting up until then for her amazing plan that had worked out so well so far. Some droplets were making it through but try as Illya might she just couldn’t…

“Eep!” With the car having hit a particularly bad bump, Illya’s seatbelt mostly helped keep her grounded, but the surprise had easily loosened things up and was helped by the said seatbelt’s tight security. Almost instantly as she shook just a tiny bit, hissing rang out in the tight quarters as it was abundantly clear from the sound and Illya’s blushing face that the little girl had just gone peepee in her diaper. Looking up between Rin and Sakura, the former had turned politely turned her head away while Sakura gave a reassuring smile, Illya feeling relieved about the situation, just like her bladder did.

Luckily for her, Exciting Splash ended up being closer than they thought and Illya squished her way out of the car in her wet diaper, just a hint of a waddle with how much she had already wet it. At least she wasn’t leaking yet and Illya toddled her way behind the pair of other girls as they approached the pool. Sakura was already on top of it though and showed off a golden pass while they passed through the turnstile. The pool was always quite impressive, but before her excitement could get to her, Illya realized something all too important. “But wait, don’t we need swimsuits?...”

“Don’t worry, I made sure to grab some before we left the store~” Sakura brought them to the changing room next, leaving Illya to wait just a little longer before she got to swim, even if she had gotten wet already. A red bikini was handed out to Rin while Sakura bought a more conservative purple one-piece for herself, but lastly, she pulled out a small package similar to the one the diapers had come in. “Here, Rin, change Illya into one of these before she gets into the pool, it’s a little tougher to get my swimsuit on.” Passing off the package to Rin as her sister had been quick to get her swimsuit on, Sakura began to undress while Illya did too, leaving the latter in just her soggy pampers.

Looking over the crinkling package in her hands, Rin couldn’t help but laugh a little as she pulled out a light blue diaper with little cartoon fishes on it. There was a bikini top as well to match it, another sign of how far ahead Sakura could think. “Before I change you though, you already soaked your current diaper a good bit, but do you have anything else you need to do in it?” 

With the two pairs of eyes on her, Illya fidgeted a little before them as she accompanied a shake of the head with a soft, “Nuh-uh.” Undoing Illya’s diaper, causing the pissy padding to plop to the ground, a few wet wipes preceded the second, thinner diaper swaddling her waist, fitting snuggly on the little girl’s big butt. It didn’t crinkle as much, but at least she could go in the pool now, allowing Rin to fit the bikini top around her petite chest as well. She could have done it herself, but Illya was finding that she felt much more babyish being unable to dress herself, letting her temporary caretakers do it instead.

With all three of the girls dressed, they headed back to the mostly empty pool, and the first thing Illya did was cannonball right into the pool with Rin futilely shielding herself while Sakura took a seat on a nearby reclining chair. Bursting out of the water, Illya’s never-ending smile emerged once again, smoothing her silver hair back as the pool water dripped from her face. Treading the water was pretty easy for her as she splashed around a bit at first before looking back toward her companions, beckoning Rin to come in with her.

The twin-tailed girl entered more gently than Illya did though, sitting on the edge of the pool before slipping into the cold water and wading over to Illya. Their height differences were made more obvious as while the water lapped at Rin’s chest, Illya was treading water. Rin’s thoughts were interrupted by a splash of water at her face, of which she swiftly returned fire to start a slew of splashing back and forth between them.

Mid-fight after a large slosh of water came over Rin, Illya found her opponent missing and turned all the way around twice before feeling something coming from below her. In a moment, her shout of surprise was mixed with laughter as her small size easily allowed her to be raised up in the air, appearing now on Rin’s shoulders. Illya couldn’t contain her giggling as she was swung around, swaying left and right and…

Suddenly, Rin froze up as she felt her back suddenly grow warmer than it should’ve been, much too warm for it to be some stray hot air and the quiet grunting followed by a sigh coming from above her was more than enough to tell her what had happened. Gripping Illya’s ankles, the mass expanded against the lower part of her neck and down her back a bit, softly crinkling and squishing. “Eeeeeew, I thought you said you were empty!” Maybe all the excitement was too much for Illya as Rin waded over to the edge of the pool, feeling the dirty bulge of the swim diaper lightly slap against her back. Gross, gross, gross!

Illya finally got off of Rin’s shoulders at the side of the pool while Sakura strolled over, having not even taken a dip yet while Illya’s fun was all too obvious from how loaded her diaper was. While she had thoroughly disgusted Rin, judging by the tsundere’s reaction, Illya was almost proud of her mess as the back of her swim diaper was pulled out and squished against her buttcheeks as Sakura seemed to be extra thorough.

“Oopsie, I didn’t realize I had to go, but it’s not too bad, is it?” Although it wasn’t a complete accident just yet, Illya had pushed the moment she felt a bit of pressure at her butt, even if the timing wasn’t exactly the best for Rin. Still, she didn’t want to stop playing just yet, especially since she was having so much fun.

For such a little girl, Sakura was always impressed with the sizes of her messes, the third one today and still so big. Although as she looked at the puppy-dog eyes of Illya’s when asked about the stinky in her diaper, she couldn’t help but want to go along with Illya’s will. “Hmm, I do have a spare swim diaper, but I don’t think you’ve used this one up enough. Let’s go play a little bit more and see if you need it then~” Sakura took Illya’s hand and led her back to the size of the pool, a pair of shadows flying over Rin before a big wave crashed over her. “Come on, it’s Illya’s birthday, let her have some fun~”

Rin just didn’t seem to be able to win today when fighting against both Sakura and Illya, where she even had a good bit of trouble with one of them. Sighing out, she resigned herself to continuing to play with then, even if she cringed a little whenever she felt a certain mushy tush brush up against her. She swore it was getting bigger and bigger, but Rin kept her mouth shut since Illya’s smile never did seem to fail as the time quickly passed by.

The trio kept on playing with each other, staying closer to the sectioned part of the pool for children as Illya’s messy butt made it tougher to swim as time went on. She even had to begin relying on a couple of pool noodles to stay up, and then eventually an inner tube, still doing her best to splash as her silver hair popped up out of the inflated ring. And yet despite her troubles with her swim diaper, Illya was still grinning, the only exceptions being as soon as she felt the need to go poopy. Her pool padding got heavier as her face scrunched up with almost no hesitation, feeling easier and easier to just push more and more filth out of her butt.

Although it only felt like five minutes overall, a whistle finally blew to signal a short break for the adults to swim without children, leaving Sakura as the youngest to leave the pool. Being in the middle of their fun, Illya and Rin joined her for the break, although Illya had a tough time getting out of the pool. Slipping and struggling to pull her messy butt up over the edge of the pool, it took Rin and Sakura both to help lift Illya out of the water and onto the sidel. On her hands and knees with her diaper drooping almost to the ground, Illya looked just like the baby she had wished to be, the moment only cut short as she worked her way back up onto her feet.

With her swim pampers sagging heavily between her legs, Illya had to waddle over to the towels with a wide gait as she had pooped it just a little past her knees at this point. It wasn’t too far in length for her petite size, but her small half-homunculi body filled her padding more than enough for the top of her butt to be showing. It had to be a miracle that the diaper was still on her waist, the tabs putting in quite a lot of work to hold up who knew however much her diaper weighed at this point. “Hehe, it’s still not too bad, i-is it?” She knew the answer way too well already, and it was plain to see for Sakura and Rin as well. Heading towards the changing room again after Sakura helped dry her off, Illya noticed Rin was bringing along the bag of supplies this time. 

It only took a tip of her head and Rin watched as Illya moved onto the gestured bench, requiring the bigger girl’s help to get her diaper up before lying down right away for a resounding squish to echo out in the changing room. Of all the places to do this, Rin found herself changing Illya’s diaper again in such a semi-public place, where anyone could walk in on her wiping the very poopy butt of the little girl. Yet Rin still carried out the duty under Sakura’s watchful eye, feeling a bit of a penetrating gaze when she thought she was done, but there was still more to clean up. Once the pressure had somewhat let up, a clean regular diaper was slid under Illya, the padding powdered and taped up as Rin could still feel Sakura watching over her shoulder. Jeez, she really had to make sure this change was good, not wanting to give Sakura any reason to punish her.

Sitting up from her change, Illya adjusted her diaper a little, listening to the crinkle as she got comfortable once again in her thicker underwear. “Thank you, Rin~ But where are my clothes?” There was only the swimsuit top and her rolled up soiled swim diaper as Illya looked around, the other pair of girls already almost having dressed again. Sitting on the locker room bench, she felt smaller than she already was as she was naked save for being swaddled in her fluffy diaper, the rest of her petite body on display. At least the pool wasn’t crowded at all and Illya saw almost no one else come through the ladies’ locker room, only a pair of whispering women whose glances made Illya blush before Sakura was finally finished dressing. 

“Raise your arms up and hold on just a moment~” Sakura rustled through her bag again, pushing aside various changing supplies to produce a plain white shirt and a pair of royal purple shortalls. With Illya’s arms over her head, she fitted the white shirt over her until a crown of silver hair popped through the collar. Right after, Sakura held out the shortalls for Illya to step in as she struggled just a little to fit them over the thick diaper, even when it hadn’t been used yet. Buckling up the suspenders, the main difference from before was that Illya looked more toddlerish than infantile now, although the bulging padding didn’t help too much with the little maturity she regained. “Anything else then before we go, you two?”

Looking up towards Rin, Illya and her shook their heads at each other before turning back towards Sakura, and the trio began cleaning up their clothes before heading out. Another pair of underwear down as Illya’s stinky swim diaper joined her soaked one from earlier in the trash as they left the pool, passing through the turnstiles once again as another taxi awaited them. Helped into the car, Illya sat between the pair of younger girls again as she didn’t even have the chance to buckle herself in before Sakura did it. “Oh, we’re going to the park now, right?” She couldn’t feel too much smaller than she already was with the childish clothing on over her thick padding, and playing on the playground sounded perfect for her. 

“Well duh, you said you wanted to go there before, but did you have anywhere else you wanted to go afterward?” Rin had done well to organize the traveling after they left the store, the taxi continuing to rumble back into the main part of town. As Illya just shook her head without another destination yet in mind, the car made its way through town, passing by various landmarks and eventually the store they were at before. At least the traffic on the way back was much lighter and it wasn’t too long before the taxi slowed down in front of a small park. To think that Illya wanted to play somewhere that was so conservative in size, but Rin wasn’t about to disagree with the birthday girl.

Illya was helped out of the taxi once more, one hand being led by Sakura while the other was led by Rin, the pair bringing her towards the lone bench. While Rin excused herself to go to the nearby bathroom, Sakura hooked her hand on the back of Illya’s shortalls before the little girl could toddle off to the playground. “Just as I thought, good thing you’re still diapered.” A hand reached through the girl’s spread legs to give it a few squishes, softly rubbing as Sakura used her other hand to open the back waistband of the diaper. “Hmm, I think you’ll be alright for now, but come back over if you have another oopsie. Well, if you notice another one, at least~” Judging by her not having seen any signs of wetting from Illya during the car ride, there was a bit of doubt as to whether Illya would even realize it before it was too late.

Blushing at the diaper check, the condition of her diaper hadn’t even crossed Illya’s mind as playing very much did instead. “Y-yeah, Sakura, I’ll try…~” Maybe she really was getting a bit too much into the role, but that was the whole point of today as she pushed that thought away. She was the birthday baby after all, and as soon as Sakura released the back of her waistband, Illya turned her focus onto the playground.

It wasn’t all too big, but she had often seen the playground while driving past throughout Fuyuki, usually on her way to someone’s house, or if she was out shopping with Sella. There wasn’t much time for her to play around though and Sella had mentioned it being a bit beneath her, yet the only thing beneath Illya now was the soaked padding on her big loli butt. And as Illya climbed the small ladder up, the cold metal of the slide squished her diaper as she slid down it, giggling all the way. Such a simple distraction for her as Illya repeated the fun, letting off crinkling and smushing as her diaperbutt hit the sand at the end of the slide.

After more than a few loops on the slide, Illya didn’t even mind as she felt the front of her diaper warmer and wetter than when she was last checked, turning her focus instead to the fact that Rin had arrived back from a nearby restroom. Intercepting her before she made it over to Sakura, Illya took her by the hand and pulled her over to the other main attraction of the park. “Come on, come on! Please push me, Rin!” Idly kicking her dangling feet after her padded rear ruffled against the seat of the swing, her smile still continued as she felt the first push at her back. “Wheeee!”

Brushing the last of the wetness of her hand off on her skirt, Rin didn’t expect to be drafted into playing with Illya again, almost a bit wary because of what happened at the pool but she put her hands on Illya’s back anyway. She could see a smart dark spot on the shortalls as Illya’s babybutt came swinging close to her face. It was just short of touching her though as Rin kept up with pushing Illya, even enjoying the sounds of Illya’s giggling as she screamed to go higher and higher. Lost in the moment, Rin recoiled back from a familiar smell as something disgusting came flying up past her face.

Even in the middle of swinging, Illya got a little too excited and only felt the start of some mushiness in her diaper after it was too late. Might as well go along with it since why would she hold it in the first place, pushing out her mess as Rin pushed her on the swing. Not much effort was needed by this point, as Illya was feeling almost like a natural at packing her pampers, listening to the squishing and squelching as her mess mushed against the seat of the swing. There was a small outburst behind her from Rin, making it easy to guess that Illya had surprised her as the swing began to slow down. It was obvious that swing time was coming to an end, leaving Illya to get a little too playful as she timed her swing and purposefully flew off of it.

Clearing the little border fence, Illya thought she could stick the landing but slipped on the sand of the playground, leaving her big messy butt to splat against the ground. A little dazed from the accident, it took Illya a moment to notice that the sand below her was growing damp as the impact loosened her bladder. It wasn’t too much, but she really had soaked her diaper too much, just as Sakura had warned her to be careful of, leaving Illya to brush off the sand before waddling over to the more-mature of her caretakers. Maybe Sakura wouldn’t be too mad at her if she acted especially cute, hoping Sakura wouldn’t notice the wet spots near her crotch.

The violet-haired girl was obviously observing everything though, although she found the birthday girl squishing down right next to her and leaning against her shoulder as well. She had seen either a shadow or a stain on her shortalls, but Sakura let it go for the moment as she shifted Illya’s head to her lap. “It’s alright, I’ll make sure to change you soon enough. Does the bathroom have a changing table, Rin?” Otherwise, she might just change Illya on the spot here, knowing that it was more public than any other changes before. At least it was in more of a secluded spot, and Sakura was only changing a baby, nothing odd at all about that, even for a big baby girl.

“Ah, actually, I don’t think there was… plus it was a pretty small bathroom anyways. We could probably just do it here if Illya’s alright with that.” She certainly needed one after what Rin had to deal with on the swing, and it wasn’t like the sound of her hitting the floor wasn’t distinct in the otherwise quiet park. “How’s that for a birthday so far, Illya? Was there anywhere else you wanted to go after you get changed or do you wa-...”

Stopped by a soft shh, her attention was drawn to the head in Sakura’s lap as the little girl softly snored. After all that she had done today, it wasn’t all too surprising that Illya was so tuckered out, falling asleep on the lap pillow in her stinky diaper. “I guess we have to wait a little longer before going home, and hopefully her diaper keeps up. I changed the last one, so it’s your turn, Sakura~” Getting a giggle and a nod in response, Rin joined the pair on the bench, patting Illya’s padded butt while watching Sakura softly pet the baby girl’s pretty silver hair. That smile of hers never left Illya’s face, the Einzbern heir’s birthday having gone much better than she could have ever expected.


End file.
